1. Field of the Invention
This invention relates to a light emitting device.
2. Background Art
A light emitting device for automobile use is used under strict conditions, and the required level of reliability has been increasingly demanding. In the case where a stoplight or taillight based on light with a wavelength near 615 nm is used in two states such as high and low brightness, the brightness degradation rate for long-term operation is required to be comparably low for both states.
If the light emitting device is formed on a translucent substrate such as GaP, optical absorption in the substrate can be reduced. Furthermore, a structure including a metal reflecting film below the light emitting layer allows emission light to be efficiently emitted outside the device. These facilitate increasing the brightness.
Furthermore, reducing crystal defects in the light emitting layer or preventing acceptors such as Zn from diffusing into the light emitting layer facilitates reducing variation in the brightness degradation rate.
JP-A-2007-123435 (Kokai) discloses a technique related to a light emitting device with small chip size and sufficient reliability. In this technique, a light emitting layer formed on a GaAs substrate is bonded to a GaP substrate, and then the GaAs substrate is removed to achieve high brightness.
However, even this technique is not sufficient to reduce degradation in a wide brightness range from low to high brightness.